Now referring to FIG. 1, there is shown a prior art embodiment of a Linear Amplification with non-Linear Components(LINC)-based apparatus 8 for amplifying a signal.
The apparatus 8 comprises a low pass filter 12, a LINC-based signal separator unit 14, a first RF conversion unit 16, a first power amplifier 18, a second RF conversion unit 20, a second power amplifier 22 and a combiner 24.
The skilled addressee will appreciate that the apparatus 8 is used to amplify a signal provided by the data generation unit 10.
The low pass filter 12 is used to perform a low pass filtering of the signal provided by the data generation unit 10.
The LINC-based separator 14 is used to receive the low pass filtered signal S(t) provided by the low pass filter 12 and to separate the signal into a first signal S1(t) and a second signal S2(t).
The skilled addressee will appreciate that the low pass filtered signal S(t) may be represented as S(t)=r(t)ejφ(t),0≦r(t)≦rMAX.
The skilled addressee will further appreciate that according to a LINC-based decomposition,
                    S        1            ⁡              (        t        )              =                            1          2                ⁢                  S          ⁡                      (            t            )                              +                        e          1                ⁡                  (          t          )                      and                    S        2            ⁡              (        t        )              =                            1          2                ⁢                  S          ⁡                      (            t            )                              +                        e          2                ⁡                  (          t          )                      with                              e          1                ⁡                  (          t          )                    -                        e          2                ⁡                  (          t          )                      =          j      ⁢                        s          ⁡                      (            t            )                          2            ⁢                                                                  r                MAX                2                                                              r                  2                                ⁡                                  (                  t                  )                                                      -            1                          .            
The first signal S1(t) is provided to the first RF conversion unit 16 while the second signal S2(t) is provided to the second RF conversion unit 20. The first RF conversion unit 16 performs a RF conversion of the first signal S1(t) and provides a first RF converted signal to the first power amplifier 18 while the second RF conversion unit 20 receives the second signal S2(t) and provides a corresponding second RF converted signal to the second power amplifier 22.
The first power amplifier 18 performs a power amplification of the first RF converted signal provided while the second power amplifier 22 performs a conversion of the second RF converted signal. The combiner 24 receives the first amplified signal and the second amplified signal and combines those signals to provide a combined signal.
The skilled addressee will appreciate that the order of low pass filtering and signal separation may be reversed such that signal separation is carried out in the digital domain and the two separated signals S1(t) and S2(t) are low pass filtered.
Referring to FIG. 2, there is shown a complex representation of the first signal S1(t), the second signal S2(t) and the low pass filtered signal S(t).
While both the first power amplifier 18 and the second power amplifier 22 operate at a maximum efficiency, since their signals have no amplitude variation, the summation in the combiner 24 dissipates the excess energy (i.e. when two signals are out of phase, the combiner 24 performs a subtraction and dissipates the subtracted energy which reduces the overall efficiency). Dissipation in heat therefore occurs. The more out of phase the signals are, the more the instantaneous efficiency decreases. The skilled addressee will further appreciate that the decrease is higher for signals having larger amplitude variations which is a drawback.
The skilled addressee will appreciate that for r(t)=rMAX, the two signals are in-phase and the efficiency is maximal.
Features of the invention will be apparent from review of the disclosure, drawings and description of the invention below.